The present invention relates to an optical disk record player and, more particularly, to a speed control circuit used in an optical disk record player operable at a variable playback speed.
Optical disk record players in which audio information is digitized in the form of pits on the reflecting surface of a disk are generally provided with a rotational servo control system so that the disk speed relative to a pickup is constant (1.3 m/s), and optical disk record players them are further capable of increasing and decreasing the tangential disk speed so that the playback speed is made variable in a range of 2-3 percent to 20-30 percent. Such variable-speed optical record players are advantageous in that the music performance speed can be varied depending on the program, but they also have a drawback of longer access time in the variable speed playback mode, particularly when the access command for searching the beginning of a program is entered during the faster-speed mode i.e., it takes a longer time before the pickup can make a track jump from the current position to the track where the beginning of the specified program exists and the playback mode can be restored to the beginning of the program. For the system implementing a track jump, refer to U.S. patent application, Ser. No. 06/487,576 now U.S. Pat. No. 4,598,394.
The main cause of the above-mentioned longer access time is that the time constant of the optical disk tracking servo system is generally set so that the pickup is positioned in a minimal time when the disk is driven at the normal speed. On this account, the access time at either the faster-speed or slower-speed of the varied speed playback mode is from 3-4 times as long as that of the normal-speed playback mode. Moreover, if a disk has scars, data reproduced from the radio frequency (RF) signal has an increased error rate than in the case of the normal speed playback mode, resulting in a further extended access time.